In the current circumstances, countermeasures against global environmental problems are recognized as a global issue. The use of natural energy such as the energy from photovoltaic power generation has attracted attention as one of the countermeasures against the problems. However, since the photovoltaic power generation is easily influenced by the weather and its output is therefore instable, various devises have been made on the effective use of the photovoltaic power generation.
For dealing with the instability of the photovoltaic power generation, a method is given in which another kind of dispersion power source such as a storage battery or a fuel cell is operated according to an operation plan. This operation plan corresponds to, for example, a control parameter enabling the appropriate control over the discharge from a storage battery whose capacity is limited. For example, when a peak-shaving system of discharging the storage battery in the excess of power demand over a predetermined power value is employed as the control system for the storage battery, this power value corresponds to the operation plan. In the operation of a combination between the photovoltaic power generation and the storage battery, in general, an operation plan is prepared for operating the storage battery for one day so that an evaluation value is the best if the power supply and demand transits as predicted, based on the transition of power demand for the following day and the forecast of weather change made in the previous day.
For example, there is a method for managing a storage battery system which adapts the operation plan to the actual weather condition. In general, the weather forecast made after the knowledge of the actual weather condition of the day is more accurate than the forecast made in the previous day. Therefore, the operation benefit could be improved by correcting the operation plan in operation based on the actual weather condition of the day if the weather forecast made in the previous day deviated.
As another example, there is a method of preparing an operation plan for a storage battery by performing simulation so that the operation plan could be corrected effectively when the forecast deviated. In this method, the forecast deviation patterns with occurrence probabilities are constructed in advance based on past data, which correspond the past cases in which the forecast value of the power supply and demand deviated by a predetermined value or more. Then, the evaluation value of an operation plan for each forecast deviation pattern is calculated by simulating the adaptation of that operation plan to the deviation of the forecast. The evaluation value obtained for each forecast deviation pattern is weighted in accordance with the probability and added to the evaluation value when the forecast does not deviate, thereby calculating the overall evaluation value. Based on the overall evaluation value, an operation plan robust to the deviation of the forecast is prepared.    Patent Literature 1: Japanese Patent No. 4245583    Non Patent Literature 1: Mitsuru KUDO, Akira TAKEUCHI, Yousuke NOZAKI, Hisahito ENDO, and Jiro SUMITA, “Forecasting Electric Power Generation of Photovoltaic Power System for Energy Network”, The Journal of the Institute of Electrical Engineers of Japan. B, Vol. 127 (2007), No. 7, pp. 847-853.    Non Patent Literature 2: Satoshi TAKAYAMA, Yuji IWASAKA, Ryoichi HARA, Hiroyuki KITA, Takamitsu ITO, Yoshinobu UEDA, Shuya MIWA, Naoya MATSUNO, Katsuyuki TAKITANI, and Koji YAMAGUCHI, “A Study on the Scheduling of Large-Scaled PV Power Station Output based on Solar Radiation Forecast”, The Journal of the Institute of Electrical Engineers of Japan. B, Vol. 129 (2009), No. 12, pp. 1514-1521.
However, conventionally, there have been no techniques capable of preparing an operation plan that can deal with any weather change.
For example, in a general operation plan preparation method of preparing an operation plan so that the evaluation value becomes the best if the weather changes as forecasted, even if the operation plan is corrected during the operation of the storage battery, the plan cannot deal with the weather change in some cases. For example, if the forecast of the weather change is wrong, the amount of power generation by the photovoltaic power generation may be smaller than expected. In such a case, the amount of discharge from the storage battery is increased more than predicted; thus, the storage battery may run out of the power during the operation. Even if the operation plan is corrected under such a circumstance, it is difficult for the storage battery to supply enough power subsequently; thus, the operation benefit of the storage battery cannot be improved.
Even in the above-mentioned method of preparing an operation plan robust to the deviation of the forecast, it is difficult to be assured that the storage battery can deal with the weather change. In this method, only the case where the forecast value of the power supply and demand is deviated by a certain value or more is considered as the forecast deviation pattern; therefore, it is not always possible to deal with the case in which the degree of the forecast deviation is small, because a small forecast deviation might cause the shortage of the power left in the storage battery that leads to a large loss. For example, the deviation that the power demand outweighs the forecast value only temporarily does not have to be considered as the forecast deviation pattern. If the amount of remaining power in the storage battery is reduced to be less than the predicted amount due to such deviation, the storage battery may be unable to deal with the weather change. In this method, the overall evaluation value obtained by weighting and adding the evaluation value of the forecast deviation pattern to the evaluation value when the forecast is right in accordance with the probability is used; therefore, for example, if the overall evaluation value is increased by the evaluation value when the forecast is right, the evaluation value of the forecast deviation pattern is relatively less taken into consideration. As a result, the operation plan which is difficult to deal with the forecast deviation pattern may be selected.